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gb640Lecture16

# gb640Lecture16 - How do we measure the proportion of genes...

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1 How do we measure the proportion of genes that are identical by descent? measures of genetic relatedness F = F is = INBREEDING COEFFICIENT – Probability That The Two Alleles Of A Gene In An Individual Are IBD measures of genetic relatedness • COEFFICIENT OF CONSANGUINITY : F ij – inbreeding coefficient of a hypothetical offspring of two individuals • allows comparison of “non-mating” individuals by means of F ij – Also called “coefficient of coancestry” – Also called “kinship coefficient” calculating the inbreeding coefficient • Pedigree method We don’t need the shaded individuals

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2 • Follow the paths of inheritance for an allele within the pedigree – What is the Mendelian probability that an allele is transmitted? calculating the inbreeding coefficient INBRED OFFSPRING: THE PRODUCT OF MATING OF FULL SIBS • Follow the paths of inheritance for an allele within the pedigree – What is the Mendelian probability that an allele is transmitted? – Example: inbreeding coefficient for the child of two half-first cousins calculating the inbreeding coefficient 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 Path: IDBA CEI
3 1/2 1/2 1/2 1/2 1/2 1/2 p(IBD) = (1/2) 6 Path: IDBA CEI 1/2 1/2 1/2 1/2 1/2 1/2 p(IBD) = (1/2) 6 second gene in A Same Path: IDBA CEI 1/2 1/2 1/2 1/2 1/2 1/2 p(IBD) = 2 (1/2) 6 inbreeding from both genes = (1/2) 5 = 1/32 • Follow the paths of inheritance for an allele within the pedigree – What is the Mendelian probability that an allele is transmitted? – Example 2: inbreeding coefficient for the child of two first cousins calculating the inbreeding coefficient Inbreeding in the offspring of first cousins A C F E D B I F = 2 [ 2 x (1/2) 6 ] = 1 / 16 Paths: IECB DFI and IECA DFI Inbreeding for a deleterious allele • Determine probability of IBD for a disease allele when the common ancestor was heterozygous for the defective allele • probability that a descendant is affected by a deleterious allele means we are interested in only one of the alleles in the ancestor – Therefore, probability of being affected is 1/2 F

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4 Other types of pedigrees INBREEDING COEFFICIENT FOR THE OFFSPRING OF A SELF-FERTILIZING PLANT F =
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